Purposes of water chemistry (quality) control in a secondary system of a pressurized water reactor (PWR) power generation plant, secondary systems of a thermal power generation plant and a fast-breeder reactor (FBR) power generation plant, and any other power generation plant (hereinafter referred to as a power generation plant) are to suppress corrosion of tubing and equipment, particularly corrosion of a heat transfer tube of a steam generator (SG) or a boiler and to prevent impurities, that lead to alkali corrosion of the heat transfer tube of the steam generator or the boiler, from being introduced therein.
As measures against the corrosion described above, water chemistry is controlled by injecting chemicals into a system to prevent deposition due to elution of ions from metal (such as iron) structural members and corrosion thereof.
For example, in a secondary system of a pressurized water reactor power generation plant, ammonia is injected to keep secondary water alkaline so as to prevent iron from flowing into the steam generator or the boiler, and a magnetite (Fe3O4) film is formed on the surface of carbon-steel tubing to suppress elution of iron and other substances so that the iron concentration in the tubing system is lowered. Further, corrosion of the heat transfer tube of the steam generator is suppressed by injecting hydrazine to reduce the amount of oxygen in the secondary water (see Patent Document 1). The measures described above are similar to those to the secondary systems of a thermal power generation plant and an FBR power generation plant. Moreover, in a main steam pipe disposed on a downstream side of the steam generator or the boiler and in a pipe through which drain or any other two-phase fluid formed of vapor and water flows, by the transfer of the injected ammonia to a gaseous ammonia, pH in the pipe is hence maintained at a high value, thereby reducing the amount of corrosion.
Further, in the power generation plants described above, as other measures to reduce the amount of corrosion of the carbon steel, there is performed a high AVT (All Volatile Treatment) method in which the pH value is maintained at 9.5 or greater, which is greater than a current value, by injecting ammonia, and also performed a method in which ethanolamine, morpholine, or any other suitable substitute amine is injected instead of ammonia, and effects of lowering impurity concentration have been confirmed.